1. Field of the Invention
The present invention relates to a photosolder resist composition which can be alkali developed, and also to a solder resist film formed using the composition.
2. Related Art
As a method for applying a solder to predetermined pares of a printed circuit board, generally employed is a method for forming a solder resist pattern on a printed circuit board. A solder resist is for applying a solder to the parts where the pattern is not formed and preventing solder from applying to the parts where the pattern is formed, and at the same time protecting the circuit in the parts where the pattern is formed.
Mounting electronic parts on a printed circuit board has recently been densified and a solder resist is required to be fine. Hence, a method for patterning a solder resist by photolithographic method tends to become a general method and for such a purpose, a liquid photosolder resist has been employed.
As such a photosolder resist composition, Japanese Patent No. 2868190 discloses a modified epoxy resin obtained by adding acrylic acid to a polyfunctional epoxy resin and adding an acid anhydride to a hydroxyl group produced by the reaction is used.
However, such a modified epoxy resin has a problem that the resin is inferior in acid resistance and alkaline resistance since the resin contains an ester bond easy to be hydrolyzed in a molecule. Therefore, there occurs a problem that defects are easily caused in a gold plating process to be carried out thereafter. Further, since brittleness is high, there is another problem of inferior thermal impact resistance. Furthermore, owing to the epoxy-modified resin, a high cost is also a problem.
Japanese Patent Laid-Open No. 191737 (2000) proposes an acrylic resin-based photosolder resist. However, since the acrylic resin-based resist has high hydrophilicity, the resist has a problem that it is inferior in water resistance and electric properties
The purpose of the invention is to provide a photosolder resist composition excellent in gold plating resistance, thermal impact resistance, and electric insulating properties and to provide a solder resist film formed using the composition.
The photosolder resist composition of the invention contains (A) a resin containing radical polymerization groups and carboxyl groups obtained by adding a cyclic ether group of a cyclic ether group-containing vinyl monomer to a carboxylic group of a radical polymer containing at least isobornyl (meth)acrylate and a carboxyl group-containing vinyl monomer as monomer units; (B) an inorganic filler; and (C) a photocurable mixture of a polyfunctional acrylic monomer (c1), compound containing a cyclic ether group (c2), and a photopolymerization initiator (c3).
The photosolder resist composition of the invention is excellent in acid resistance and alkaline resistance, and consequently excellent in gold plating resistance and at the same time in thermal impact resistance and electric insulating properties since the composition contains the above-described resin (A), inorganic filler (B) and photocurable mixture (C).
The resin (A) is preferable to have double bonds of 0.1xc3x9710xe2x88x923 to 3.0xc3x9710xe2x88x923 mol/g. In addition, the content of the carboxyl group (acid value) is preferably 30 to 200 mgKOH/g.
The ratio of the carboxyl group in the resin (A) and the cyclic ether group in the photocurable mixture (C), that is, in the compound (c2) is preferably (1.3/0.7) to (0.7/1.3) by mole.
Further, the solder resist composition of the invention may further contain a coloring pigment.
The content of the inorganic filler (B) is preferably 5 to 75 parts by weight in 100 parts by weight of solid content of the entire photosolder resist composition of the invention.
Further, in the invention, the resin (A) may be neutralized by a base and made water-soluble.
The solder resist film of the invention is obtained by applying the photosolder resist composition of the invention to a substrate, drying at 50 to 90xc2x0 C., exposing by activation energy beam, removing and developing non-exposed parts with an alkaline washing solution, and heating and curing the photocured parts at 140 to 170xc2x0 C.
Hereinafter, detailed description will be given respectively for the resin (A), i.e. the first component, the inorganic filler (B), i.e. the second component, and the photocurable mixture (C), i.e the third component, of the photosolder resist composition of the invention.
The first component contained in the photosolder resist composition of the invention is a resin containing a radical polymerization group and a carboxyl group, and can be obtained by ring-opening addition of a cyclic ether group of a cyclic ether group-containing vinyl monomer to a carboxylic group of a radical copolymer containing at least isobornyl (meth) acrylate and a carboxyl group-containing vinyl monomer as monomer units. The content of isobornyl (meth)acrylate contained in the resin (A) is preferably 10 to 50% by weight and further preferably 15 to 35% by weight. If less than 10% by weight, the tack property and the thermal resistance may be insufficient and if more than 50% by weight, the brittleness may become too high.
Examples of the carboxyl group-containing vinyl monomer are acrylic acid, methacrylic acid and the like. As an example of the cyclic ether group-containing vinyl monomer, glycidyl methacrylate is typical one and also usable is 3,4-epoxycyclohexyl methacrylate, disclosed in Japanese Patent Laid-Open No. 191737(2000). However, from a viewpoint of an addition reactivity, the material cost and the like, glycidyl methacrylate is especially preferable to be used.
The resin (A) containing a radical polymerization group and a carboxyl group contains at least one radical polymerization group and carboxyl group in one molecule, in which the double bonds are preferably 0.1xc3x9710xe2x88x923 to 3.0xc3x9710xe2x88x923 mol/g and further preferably 1.0xc3x9710xe2x88x923 to 3.0xc3x9710xe2x88x923 mol/g, and the content of the carboxyl group is preferably 30 to 200 mgKOH/g. If the double bonds are less than 1.0xc3x9710xe2x88x923 mol/g, the photocurable property of the obtained resist may become insufficient so that there is possibility to result in deterioration of adhesion and thermal resistance at the time of development, and if they are more than to 3.0xc3x9710xe2x88x923 mol/g, not only the film strength may become brittle but also the resolution property may be deteriorated. Further, if the content of the carboxyl group is less than 30 mgKOH/g, the alkaline development property may be deteriorated, and if it more than 200 mgKOH/g, even the exposed parts may be dissolved. The double bonds are further preferably 1.5xc3x9710xe2x88x923 to 2.7xc3x9710xe2x88x923 mol/g and the content of the carboxyl group is further preferably 70 to 120 mgKOH/g.
The number average molecular weight of the resin (A) is preferably 2,000 to 40,000. If it is less than 2,000, the heat resistance of the obtained resist may be insufficient, and if it is more than 40,000, the viscosity may become too high and there sometimes occurs a problem on the workability at the time of producting the composition.
In the invention, a base may be added to the resin (A) to neutralize the carboxyl group so as to use the resin (A) as an aqueous solution. The above-described base is not particularly restricted and usable are well-known neutralization agents for carboxylic group, for example, inorganic substances such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; and amine compounds such as triethylamine and dimethylethanolamine. The amount of the above-described base is properly determined corresponding to the molecular weight of the resin (A) and the content of the carboxyl group and may be proper to make the resin (A) water soluble and, for example, the amount may be set to be sufficient to neutralize 30 to 200% (0.3 to 2 mole) of that of carboxyl group.
The second component contained in the aqueous photosolder resist composition of the invention is an inorganic filler. The inorganic filler is used to improve the heat resistance of the resist and usable are well known substances such as barium sulfate, finely powdered silicon carbide, amorphous silica, talc, mica and the like. Additionally, the above-described inorganic filler includes a well-known fire retardant. Incidentally, the above-described inorganic filler can be dispersed by a known method in the presence of the resin (A)
The amount of the above-described inorganic filler is determined as a ratio to the entire solid content of the photosolder resist composition of the invention. The ratio will be described later in the description of the photosolder resist composition.
The third component contained in the photosolder resist composition of the invention is a mixture of a polyfunctional acrylic monomer (c1), a compound containing cyclic ether group (c2), and a photopolymerization initiator (c3).
 less than Polyfunctional acrylic monomer (c1) greater than 
The above-described polyfunctional acrylic monomer (c1) may be any compound having two or more polymerization groups (for example, acryloyl group or methacryloyl group) in one molecule, and it is possible to make photocuring for patterning by including the polyfunctional acrylic monomer (c1). Practical examples of the above-described polyfunctional acrylic monomer (c1) are pentaerythritol triacrylate, dipentaerythritol pentacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexacrylate and methacrylates corresponding to the above-described acrylates. They may be used solely or in combination of two or more of them.
 less than Cyclic ether group-containing compound (c2) greater than 
The above-described compound containing cyclic ether group (c2) is to be heated to cause curing reaction with the carboxyl group of the resist composition [mainly of the resin (A)]. Examples of those which the cyclic ether group is glycidyl are well-known compounds such as bisphenol type, phenol novolak type, cresol novolak type, epoxylated polybutadiene and the like. A variety of compounds are commercialized as those having alicyclic epoxy group and examples are Celloxide series, Epoleed series, Cyclomer series and their polymers sold by Daicel Chem. Ind., Ltd. Further, as those having oxetane group, sold by Toagosei Chemical Industry Co., Ltd. are Aron Oxcetane series. Among them, taking the storage stability of a mono-liquid state mixture of (A), (B) and (C) into consideration, preferable are those having 2 or more alicyclic epoxy groups or oxetane groups in one molecule, whose reaction rate is slow as compared with those having glycidyl groups and especially preferably are those having 3 or more of the groups.
 less than Photopolymerization initiator (c3) greater than 
As the above-described photopolymerization initiator (c3), well-known compounds may be used. Practical examples are benzoin and benzoin alkyl ethers such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether and the like; acetophenones such as acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone and the like; aminoacetophenones such as 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butancne-1, N,N-dimethylaminoacetophenone and the like; anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone and the like; thioxanthones such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-diisopropylthioxanthone and the like; ketals such as acetochenone dimethyl ketal., benzyl dimethyl ketal and the like; benzophenones or xanthones such as benzophenone, 4,4xe2x80x2-bisdiethylaminobenzophenone and the like; and phosphine oxide such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide. These compounds may be used solely or as a mixture of two or more of them and further, a tertiary amines such as triethanolamine and a photoinitiator promotor such as ethyl dimethylaminobenzoate may be added to use.
The weight ratios of the above-described polyfunctional acrylic monomer (c1), compound containing cyclic ether group (c2), and photopolymerization initiator (c3) in the photocurable mixture contained in the photosolder resist composition of the invention are determined as the ratios to the entire solid content contained in the photosolder resist composition of the invention. The ratios will be described later in the description of the photosolder resist composition.
Further, the above-described photocurable mixture may further contain a compound containing an amino group such as dicyanediamide, and melamine and blocked isocyanate and the like which are reacted with a cyclic ether group, other than the above-described components.
The photosolder resist composition of the invention contains (A) a resin containing radical polymerization groups and carboxyl groups obtained by adding a cyclic ether group of a cyclic ether group-containing vinyl monomer to a carboxylic group of a radical copolymer containing at least isobornyl (meth) acrylate and a carboxyl group-containing vinyl monomer as monomer units; (B) an inorganic filler; and (C) a photocurable mixture of a polyfunctional acrylic monomer (c1) a compound containing a cyclic ether group (c2), and a photopolymerization initiator (c3).
The photosolder resist composition of the invention can be obtained by mixing the above-described components by a method well known by skilled in the art. At that time, the ratios of the respective components preferably satisfy the following conditions in order to improve the capabilities of the resist composition and the resist obtained from the composition.
At first, the ratio of the carboxyl groups of the resin (A) to the cyclic ether groups of the photocurable mixture (C) is preferably from (1.3/0.7) to (0.7/1.3) by mole ratio. If the ratio is out of the range, the cross-linking degree may not be increased, thereby resulting in insufficient heat resistance. Further, the ratio is more preferably from (1.15/0.85) to (0.85/1.15).
Next, the inorganic filler (B) is preferably in a ratio of 5 to 75 parts by weight to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention. If less than 5 parts by weight, in some cases, the effect of preventing the heat resistance and curing shrinkage becomes insufficient and if more than 75 parts by weight, in some cases, the development property is deteriorated. The ratio is more preferably 15 to 60 parts by weight.
The polyfunctional acrylic monomer (c1) contained in the photocurable mixture (C) is preferably in a ratio of 2.0 to 15.0 parts by weight to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention. If less than 2.0 parts by weight, in some cases, the photocurable property is insufficient and if more than 15.0 parts by weight, in some cases, the cold heat impact resistance is deteriorated.
On the other hand, the photopolymerization initiator (c3) contained in the photocurable mixture (C) is preferably in a ratio of 0.5 to 7.5 parts by weight to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention. If less than 0.5 parts by weight, in some cases, the photocurable property is insufficient and if more than 7.5 parts by weight, in some cases, the hardness of a film is possibly lowered since the polymerization degree is too low at the time of photocuring. The ratio is more preferably 1.0 to 5.0 parts by weight.
The compound containing the cyclic ether group (c2) contained in the photocurable mixture (C) is preferably in ratio of 5.0 to 15 parts by weight to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention. If less than 5.0 parts by weight, in some cases, the heat resistance is insufficient owing to low curing density and if more than 15 parts by weight, in some cases, the cured film becomes brittle. Further, the ratio is more preferably 7.5 to 12.0 parts by weight.
The photosolder resist composition of the invention may contain an internal solvent other than the above-described components based on necessity. The solvent is used as an assisting agent for making a film even and capable of dissolving the oil components among the above-described components therein and has a boiling point of 120 to 250xc2x0 C., preferably 135 to 200xc2x0 C., and practical examples are propylene alycol diacetate, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate and the like. In the case of using such an internal solvent, it is added preferably in 100 parts by weight or lower, more preferably in 25 parts by weight or lower, to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention.
Further, the photosolder resist composition of the invention may contain a coloring pigment. As the coloring pigment, usable are well-know pigments such as phthalocyanine copper, phthalocyanine chloride, Quinacridine Red and the like. In the case of including a coloring pigment, the pigment is added preferably in a ratio of 0.02 to 4.0 parts by weight to 100 parts by weight of the entire solid content of the photosolder resist composition of the invention. If less than 0.02 parts by weight, in some cases, the coloring property is insufficient and if more than 4.0 parts by weight, in some cases, the film is possibly parted at the time of development owing to deterioration of the photocurable property. The ratio is more preferably 0.05 to 1.0 parts by weight.
The photosolder resist composition of the invention can be obtained by mixing the above-described components and generally, at first the resin (A) is produced and then the inorganic filler (B) and if necessary a coloring pigment are added to the resin and then the respective components of the photocurable mixture (C) and an internal solvent if necessary are added and the resulting mixture is made uniform. In form of products, possible are two-liquid mixture type ones consisting of a mixture of the resin (A) and the inorganic filler (B) and the photocurable mixture (C), and one-liquid type ones containing all of the resin (A), the inorganic filler (B) and the photocurable mixture (C).
The photosolder resist composition of the invention may be used while being emulsified by neutralizing the resin (A) with a base and making the resin water soluble, removing the solvent contained in the resin based on necessity, adding the inorganic filler (B) and a coloring pigment if necessary and dispersing them, and after that, adding the respective components of the photocurable mixture (C) and an internal solvent based on necessity. Since the water-soluble photosolder resist composition can be used while using a lessened amount of a solvent, it is extremely advantageous from the viewpoint of scarce malodor emission and good working environments. The particle diameter of the emulsion of the photosolder resist composition of the invention obtained in such a manner is preferably 0.1 to 10.0 xcexcm and more preferably 0.3 to 2.0 xcexcm in the surface area average particle diameter. If it is smaller than 0.1 xcexcm, it may be difficult to produce and if it is larger than 10.0 xcexcm, precipitation or flocculation of particles sometimes takes place.
The ratio of the solid content of the photosolder resist composition of the invention is preferably 30 to 90% by weight and more preferably 40 to 70% by weight. If it is less than 30% by weight, the economical efficiency may be slight and if it is more than 90% by weight, it may be difficult to produce since the viscosity becomes too high.
The photosolder resist composition of the invention is applied to a base material such as a substrate and generally dried at 50 to 90xc2x0 C. After drying, activation energy beam such as UV ray is radiated to carry out exposure and the non-exposed parts are developed and removed with an alkaline washing solution and further the photocured parts are heated at, for example, 140 to 170xc2x0 C. to promote thermal curing and obtain a solder resist film.